Gas-powered guns, particularly pistols, have often incorporated barrels that unlatch and tip up as part of their design so as to facilitate loading and cleaning. However, that feature necessarily creates a potential trouble-spot because the otherwise continuous gas passage between the source of gas supply and the barrel now has a point of interruption at the interface between the barrel and the valve body that must be adequately sealed when the barrel is closed so that gas does not escape during the firing action. Furthermore, if the barrel is not returned to the exactly proper position before firing, the accuracy of the gun will be sacrificed.